This invention relates in general to promoters for use in transgenic plants and more particularly to the tissue-specific expression and synergistic interactions of subdomains of the 35S promoter of cauliflower mosaic virus (CaMV).
Through the use of recombinant DNA technology and genetic engineering, it has become possible to introduce desired DNA sequences or genes into cells to allow for the expression of proteins of interest. This technology has been applied to plants to provide plants having unique characteristics. In order to obtain adequate expression of a gene inserted into a plant cell, a promoter sequence operable in plant cells is normally required. The 35S promoter of cauliflower mosaic virus (CaMV35S) is one such promoter and acts as a strong constitutive promoter in most organs of transgenic plants (Odell et al., 1985; Jensen et al., 1986; Jefferson et al., 1987; Kay et al., 1987; Sanders et al., 1987). The upstream region from -343 to -46 (upstream of the "TATA" box nucleotides) of the CaMV35S promoter has been shown to function in an orientation and distance independent manner (Fang et al., 1989; Nagy et al., 1987). It has also been previously shown that this enhancer is composed of at least two domains able to confer tissue-specific and developmentally regulated expression in transgenic plants (Benfey et al., 1989). One of the domains (-90 to +8) has been termed domain A (which also contains the TATA region from -46 to +8) and is able to confer expression principally in root tissue (Benfey et al., 1989). A sequence motif of a tandem repeat of TGACG has been identified within domain A that binds a factor found in nuclear extracts from tobacco (Lam et al., 1989). A cDNA clone for a factor that binds to this motif has also been isolated (Katagiri et al., 1989). The level of the RNA that hybridizes to this cDNA is 5 to 10 fold higher in the root than in the leaf (Katagiri et al., 1989). Domain A, therefore, appears to be able to confer expression in root tissue because it contains a sequence motif that interacts with a factor that is found predominantly in root. Previous work has also indicated that domain A may play a role in potentiating transcription when associated with other cis-elements. In particular, domain A has been shown to be able to interact synergistically with a region further upstream to potentiate transcription in leaf (Fang et al., 1989). The second domain (containing nucleotides -343 to -90) has been termed domain B and has been shown to confer expression in most cell types of leaf and stem as well as in vascular tissue of the root (Benfey et al., 1989).
It would be advantageous to the development and use of transgenic plants to be able to direct tissue-specific expression of genes inserted in these plants. While the general tissue targets of domain A and domain B of the CaMV35S promoter are known, defining the tissue-specific and developmentally regulated expression patterns conferred by isolated subdomains of the CaMV35S promoter, if such exist, would provide greater insight into the utility of the promoter in transgenic plants.
It is therefore a primary object of the present invention to provide the tissue-specific and/or developmentally regulated expression of chimeric plant genes, by the use of novel promoters comprising subdomains of the CaMV35S promoter.
It is another object of the present invention to provide novel promoters for use in transformed plant cells, transgenic plants and seeds that are comprised of a subdomain or combination of subdomains from the CaMV35S promoter.